Bar stock such as round rods and other shapes can be made by rolling an elongated workpiece between rolls having at least one caliber or channel formed in the circumference of the roll.
A shape-determining groove or channel is one which, with a registering channel of another roll will define a passage between the rolls through which the workpiece can pass and which together form the closed periphery of the passage which has both the cross section and dimensions of the bar stock to be made.
It is known to provide a pair of such rolls with registering grooves defining a closed passage and to place the rolls together so that they are urged against one another with a prestressing force which, at least in part, controls the dimensions of the passage.
From German Patent DE-PS No. 741,884, it is known that a bending of the shaping rolls during the rolling of strip can be reduced by the use of so-called caliber rolls, i.e. rolls which have grooves defining the caliber of the product made, i.e. the passage through which the workpiece passes. In this system, a passage is formed which has the width of the strip to be rolled and adjacent this passage and hence the grooves defining same, the juxtaposed rolls are formed with end regions which bear against one another with a prestressing force exceeding the rolling force.
While this technique does reduce the bending of the rolls to a certain extent it has been found to be insufficient to completely eliminate such bending.
In German Patent Document - Open Application DE-OS No. 34 33 300, the rolling of bar stock between rolls which define the caliber or passage is described as being associated with the application of a prestressing force of the rolls against one another adjacent the caliber grooves with a prestress that significantly exceeds the rolling force.
The purpose of this prestress is to maintain the dimensions of the rolled product by preventing the expansion of the roll set defining the caliber. In this case, any change in the rolling force is effectively counteracted by the prestress.
It is possible with that system as well by controlling the applied or pressing force of the rolls against one another and thereby varying the prestressing force to vary the degree of elastic flattening of the mutually abutting surfaces of the rolls and thereby change the dimensions of the passage and, as a consequence the dimension of the rolled product. In this case, the change in the prestressing force can be used as an adjustment or setting for direct control of the dimensions of the product.
A disadvantage with such setting and control operations is that the flattening of the rolls requires such high forces that the prestressing force may have to be so much higher than the rolling force that the results are detrimental to effective operation of the system. For example, since the mill frame must withstand the high pressing forces which are applied, the mill must be dimensioned far more massively.